Thin-leaved Coneflower is an erect native biennial or short-lived perennial, growing to 5+ feet tall (but usually around 3 to 4 feet) on branching stems that are red in color in the upper sections and with whitish hair on the upper parts of the stems. The text here treats var. triloba, the variety native to Minnesota.
The leaves are thin and rough on both sides, lanceolate to ovate in shape. Upper leaves have few teeth, are smaller and stalkless. Lower stem leaves can be up to 6 inches long and can be 3-lobed with coarse teeth and have long stalks.
The floral array consists of branched clusters of one to several flower heads atop individual stems.
Flower heads are 1 to 1-3/4 inches wide with a purplish-brown central disc, 1/3 to 1/2 inch wide that is domed, consisting of numerous fertile disc florets that have dark purplish corolla tubes with yellow green bases. The tubes have 5 triangular lobes at the tip. The single style is branched at the tip. Five stamens surround the style and both style and stamens are exserted from the corolla tube when the floret opens. Disc florets are surrounded by 6 to 12 (8 to 15) oblong to ovate, sterile yellow ray florets whose laminae are 8 to 17 mm long. Beneath and around the head are green floral bracts (phyllaries) arranged in 2 series. These have very fine hair.
Seed: Fertile disc florets produce a dry 4-angled cypsela, somewhat crown shaped, 1.9–2.8 mm long, that does not have any fluffy pappus. Dispersion is by scattering from the dry seed head. Seeds need 30 days of cold stratification for germination.
Varieities: Three are recognized: var. pinnatiloba where some of the stem leaves have 5 to 7 lobes and then two varieties where the stem leaves usually have 3 lobes - var. rupestris where the ray laminae are 18 to 30 mm long and the central disc is 15 to 22 mm in diameter; and var. triloba where the ray laminae are only 8 to 17 mm long and the central disc is 10 to 15 mm in diameter. The last is the variety native to Minnesota.
Habitat: Thin-leaved Coneflower grows best in fertile soils with wet to moderate moisture in full sun; sites along streams and rivers are the natural habitat. Partial shade is tolerated, drought tolerance is moderate. The root system is fibrous.
Names: The genus Rudbeckia, is named after the Swedish father and son, - O. J. and O. O. Rudbeck, who were professors of botany and predecessors of Linnaeus. The species name, triloba, refers to the lower leaves which can have 3 lobes. The author name for the plant classification, 'L.', refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: Two others of the Rudbeckia genus that are similar are Black-eyed Susan, R. hirta, and Sweet Black-eyed Susan, R. subtomentosa. R. hirta is shorter, has more yellow ray florets, a flattened dome of disc florets, leaves without lobes and lacks the red stems. R. subtomentosa has the same height, but the flower heads have more ray florets that have more pointed tips, a more flattened dome of disc florets and also lacks the red upper stems. As to the plethora of common names, this is unfortunate, and shows the virtue of unique scientific names - see notes at page bottom of the various names applied just within Minnesota.
Above: 1st photo - The central disc is domed. 2nd photo - The sterile yellow rays are ovate in shape with blunt tips.
Below: 1st photo - The phyllaries are in 2 series, with fine hair; the lower ones overlapping and longer than the uppers. 2nd photo - The fertile disc florets have yellow-green bases, purplish upper corolla tubes with 5 lobes.
Below: 1st & 2nd photos - Upper stem leaves are without stalks. Note the fine hair on the surfaces of the leaves and on the stem. The stem in the upper sections is usually a deep reddish color.
Below: 1st photo - A lower leaf with its long stalk. The lower stem segment is usually green.
Below: The lower leaf with the characteristic 3 lobes and coarse teeth.
Notes: Thin-leaved Coneflower is not indigenous to the Garden. It has been in the Garden in previous times: Eloise Butler first planted it on Oct. 1, 1923 with plants from Lake Geneva, WI, then added more in 1926 and sowed seeds in 1930. Martha Crone planted it in Oct. 1945 and then planted seeds in 1948, '49 and '53. It was listed on her 1951 census. The plant was restored to the Garden during the 2008 restoration of the section of upland near the back fence. R. triloba is native to the south central plains states and the eastern half of the U.S. except Florida and New England. In Canada it is found in Quebec and Ontario. The species native in our area is R. triloba (L) var. triloba. Within Minnesota it is rare in the wild, being known currently from only 5 native populations in 2 SE counties and those populations are quite small. RARE in the Wild: It is listed on the MN DNR's "threatened" list. Other counties have reported the plants, but those have been determined to be in old gardens or escapees from gardens, not native. The plant has been widely sold in the nursery trade for home gardens and landscape uses. SE Minnesota is at the NW limit of range for this plant. This is a special plant for the Garden to maintain.
Four species of Rudbeckia are considered native to Minnesota: R. laciniata, Green-headed (or Tall) Coneflower; R. hirta, Black-eyed Susan; R. triloba, Three-leaved (or Thin-leaved) Coneflower; and R. subtomentosa, Sweet Coneflower (Sweet Black-eyed Susan), although the latter is considered either an introduction or an extension of its normal range from Iowa and southern Wisconsin, as there is only one known population in the wild, in Mower County. The nursery trade has produced cultivars of Green-headed Coneflower, known commercially as Golden-glow, which occasionally escapes from cultivation
The Common Names: The choice of many names for the plant is unfortunate. Most sources refer to it as Brown-eyed Susan. This includes the University of Minnesota Herbarium. They also list as an alternate, Three-leaved Coneflower, which agrees with what the DNR names the plant. This name however, is not descriptive of the plant as the the leaf is not in 3 parts as that name implies, but instead, the lower leaves have 3 lobes. The Garden's use of 'thin-leaved' at least matches part of the leaf description. Brown-eyed Susan is more generally applied.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"